add_decal · Loenn MCP: Risk & Policy

WHAT IT DOES

What add_decal does on Loenn

AI agents use add_decal to create or update resources in Loenn — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Loenn environment.

WHY IT NEEDS A POLICY

Why add_decal needs a policy

The tool creates or modifies map data by adding a decal (a visual/graphical element in game maps). This is Write-category because it adds content reversibly and cannot irreversibly destroy data. It lacks execution or financial implications.

From the tool's definition Tool name 'add_decal' combined with sibling tool pattern 'add_entity', 'add_room', 'add_trigger' indicates this creates/modifies map content. The server description states it enables agents to 'edit...Celeste .bin map files'.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

add_decal Rate-limited

add_decal stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "add_decal": {
      "limits": [
        {
          "counter": "add_decal_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Loenn, so you can run agents against it safely.

FAQ

Questions about add_decal

What does the add_decal tool do? +

add_decal. It is categorised as a Write tool in the Loenn MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on add_decal? +

Register the Loenn MCP server in PolicyLayer and add a rule for add_decal: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Loenn. Nothing to install.

What risk level is add_decal? +

add_decal is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit add_decal? +

Yes. Add a rate_limit block to the add_decal rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block add_decal completely? +

Set action: deny in the PolicyLayer policy for add_decal. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides add_decal? +

add_decal is provided by the Loenn MCP server (magedeline/loenn-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.